The invention relates to an energy filter for monochromizing a charged particle beam in a charged particle beam apparatus and to a charged particle beam apparatus provided with such an energy filter.
Chromatic aberration is one of the main factors that limits the resolution in charged particle beam apparatus such as ion beam microprobes, low-voltage electron microscopes, high resolution electron microscopes especially when spherical aberration is corrected, electron beam holography apparatus etc.
Chromatic aberration can be corrected for at least in principle with the aid of a quadrupole system or a non-dispersive Wien filter system. Such systems, however, require an extreme stability of the electro-magnetic fields so that practizising has not been realised up to now. A monochromator comprising a system of cylindrical mirror analyzers has also been proposed, a drawback thereof is the low dispersion obtainable in a filter with an acceptable lengthening of the apparatus to be corrected